Study On Interface Protection And Stability Of Lithium Metal Anodes

Due to limitations in the theoretical capacity of existing materials,it has become increasingly difficult for existing lithium-ion batteries to meet the higher energy density demands from the market.Lithium metal batteries have received widespread attention due to their high theoretical capacity and have become a strong candidate for next-generation energy storage systems.However,the poor stability of lithium metal makes it difficult to be directly used in practical battery systems.Previous studies on improving the stability of lithium metal anodes have focused on the electrochemical stability improvement.However,from the perspective of the practical use of lithium metal batteries,the poor environmental stability of lithium has greatly increased the difficulty of operation and the cost of use.In recent years,more and more researches focus on a balanced improvement of lithium metal anodes between electrochemical stability and environmental stability.Based on this,this article has carried out a modification study on the surface protection of lithium anode,and the specific contents are as follows:(1)Research on building a polymer protective layer to improve the stability of lithium metal anode.The polyvinylidene fluoride(PVDF)is bonded to the surface of the lithium metal through a heating and pressing process at a temperature slightly higher than the melting point of the two.The thermodynamic test proves that PVDF is chemically stable during the heating and pressing process.The PVDF protective layer with abundant polar functional groups has a structure of porous surface and dense interior and is in close contact with lithium metal,which can guide the rapid transmission of lithium ions,reduce surface side reaction and inhibit dendritic growth.Tests under air exposure show that the protective layer can effectively inhibit air corrosion of lithium metal.Further electrochemical characterization tests prove that the PVDF protective layer increases the ion migration number and has electrochemical stability.In addition,the cycling stability of the lithium metal anode with PVDF protective layer has been significantly improved in symmetrical cells,half cells and full cells.(2)Based on the experiments above,in order to better regulate the lithium nucleation properties and optimize the interface of the lithium metal anode,tin oxide nanoparticles are selected as the dopant to obtain a composite lithium metal anode protective layer.During the heating and pressing process,part of the tin oxide will be lithiated,forming a lithium-philic lithium-tin alloy on the surface of the lithium metal.At the same time,the tin oxide filler inside the composite protective layer enhances the mechanical properties of the protective layer.The modified lithium metal also has air stability,and the close-contact protective layer can effectively inhibit the corrosion of metal lithium by the air for up to 2hours.After the mechanical properties and electrochemical tests of the composite protective layer with different tin oxide doping amounts,a suitable tin oxide nanoparticle introduction amount was selected to be 30wt%.Through the comparison experiment of the performance of tin oxide and copper oxide dopants,the importance of the lithium-philic sites to the protective layer is demonstrated.The protected metal lithium is used as anode in a full-battery system for testing.The experimental results show that the surface-modified lithium anode remains almost unchanged capacity during long cycles and has a higher discharge capacity than the original lithium anode under different cycling rates.